In addition to the grid, DROP3D requires an air solution as input. The recommended way to assign the grid and the air solution files as well as the flow reference conditions to DROP3D is to drag and drop the configuration icon of the FENSAP run onto the DROP3D configuration icon:
You can also set (or reset) these files using the Input files tab in the configuration window.
The grid file is then read to detect the boundary conditions.
Note: If the grid is replaced, it is imperative to review the parameters assigned to the boundary conditions, described in DROP3D Boundary Conditions.